A plug door installed in a doorway of a vehicle has conventionally been known. Such a plug door executes a plug operation in which, after moving in the closing direction to cover the doorway, the plug door moves toward the inside of the vehicle in the vehicle width direction to bring the doorway and the door leaf into tight contact with each other.
A plug door lock device for mechanically locking the door leaf to the vehicle subsequent to the plug operation is mounted in the plug door described above. Japanese Unexamined Patent Publication No. H06-262945, for example, discloses a plug door device (plug door lock device) that has lock arms provided on the upper and lower sides of the door leaf. When a motor is driven in this plug door lock device, a latching roller provided at a tip end part of each lock arm fits into a groove of a latching opening formed on the door (door leaf). The lock arms therefore pull the door leaf toward the vehicle. Consequently, as a result of the plug operation of the door leaf, the space between the doorway of the vehicle and the door leaf is kept airtight. In this airtight state, the door leaf is locked to the vehicle.
Incidentally, the plug door lock device described above is provided with a universal joint for the purpose of operating the two lock arms on the upper and lower sides of the door leaf by means of a single motor. For this reason, the plug door lock device has a complicated structure. In addition, in case of failure in the motor, the failure has an impact on both of the two lock arms.